1. Field of the Invention
Embodiments of the present invention relate to a hard disc drive (HDD) data read control apparatus, medium, and method, and more particularly, to a HDD data read control apparatus, medium, and method for reading data from a disc having a non-uniform track-to-track spacing
2. Description of the Related Art
A hard disc drive (HDD) may include a plurality of magnetic heads linked to rotating discs. Each head writes information by magnetizing a portion of a disc or reads information by detecting a magnetic field from a portion of the disc.
Each head is typically assembled with a flexure beam to form an assembly called a head gimbal assembly (HGA). The HGA may be assembled with an actuator arm having a voice coil assembled with a magnet assembly, with the voice coil and the magnet assembly forming a voice coil motor (VCM), which can move the head across a disc by activating the actuator arm.
Information may typically be stored on tracks concentrically formed on the disc. Here, the VCM may move the head from a certain track to another track in order to access data stored on the disc. Each track contains a plurality of sectors, each having a servo area and a data field.
A tracking servo of the HDD may control the head to move along a track centerline. The tracking servo may control the head to follow the track centerline by reading servo burst signals from the disc, computing a head location with respect to a track centerline, and controlling the VCM with reference to the computation result.
Servo information including the servo burst signals, as an example, may be written on the disc by a servo writer in a manufacturing process of the HDD.
Along with recent increases of high data capacities, the number of tracks per inch (TPI), which denotes the track density, has also been increasing. Accompanying the increase of track density, track-to-track spacing has necessarily been narrowed. Accordingly, the uniformity of the track-to-track spacing has been important. However, in a servo writing process of the HDD, a problem may occur in that the track-to-track spacing may be narrower or wider, i.e., non-uniform, at an arbitrary location, e.g., due to a plurality of reasons such as a mechanical errors, vibrations, resonance and/or write intensities.
This non-uniformity of the track-to-track spacing impedes correct tracking of the head by causing discontinuous information to be provided from the non-uniform location. For example, expandability of a write field may be impeded by a discordance between an expected head location, determined by an offtrack amount controlled by a servo or a magneto-resistive (MR) offset of the head, and an actual location of the head.
Here, in a case of an MR head, where the write and read heads are separated, the distance between the center of the write head and the center of the read head may vary according to head locations on the disc, so-called the MR offset. As a result, in order to make the read head of the MR head exactly follow tracks written by the write head, the location of the read head should be compensated to take into consideration an MT offset of a relevant track.
To this end, in a manufacturing process of the HDD, MR offsets may be measured along several locations on the disc and stored in a memory. Thereafter, the HDD can compensate for differing locations of the read head by referencing the stored MR offsets during read operations. If the head lays between sampling locations when a respective MR offset is predicted, the MR offset may be calculated by an interpolation scheme using MR offsets measured at adjacent sampling locations, for example. Further discussions of such MR offsets have been set forth in Korean Patent publication No. 2004-32382 (Apr. 17, 2004), Japanese Patent Publication No. 1993-234283 (Sep. 10, 1993) and U.S. Pat. Publication No. 6,188,538 (Feb. 13, 2001).
However, such interpolation schemes are based on the assumption that track widths are uniform. Accordingly, if the track widths are non-uniform, the interpolation MR offset compensation acc scheme cannot be normally performed.
If the track-to-track spacing is narrower than a normal spacing, a fatal result may occur where detected written data may be incorrectly detected due to the prominent occurrence of an adjacent track erasure effect, as a result of an incorrect tracking in an adjacent track. This adjacent track erase effect is increased by the accumulation of the same accompanied with frequent updates on the same track. As track densities further increase, this track-to-track spacing non-uniformity becomes a more inevitable problem.
Conventionally, to solve these problems generated due to the track-to-track spacing non-uniformity, such non-uniformities may be compensated by detecting and recording all locations on a disc where the track-to-track spacing is non-uniform or failure-processing the disc when the number of non-uniform track-to-track spacings exceeds a predetermined threshold.
However, in these conventional methods, according to the further increases in track density, the time required for such a track-to-track spacing non-uniformity test becomes greater and greater, and thus, the available yield of HDDs decreases.